Some Contemporary Advances in Physics IV 



By KARL K. DARROW 



ri.osiNr, Tin-: Spkctium Cap Bi'.twf.fn the Infra-khd 

 AND THE Hertzian Regions 



AN electrical circuit hax'ing a natural oscillation-frcc|uc'iic\' an\- 

 ■ where below 10' can be constructed by anyone with suitable 

 condensers, inductance-coils, and a few feet of wire at his disposal. 

 It can be set into oscillation by abruptly closing it when the condenser 

 is charged, by coupling it to an audion, or otherwise; and the wa\c's 

 which it radiates while oscillating can be detected and measured, at 

 least when the frequency exceeds 10". Thus it is possible to generate 

 perceptible electromagnetic waves of frequencies up to 10**, and hence 

 of waxelengths down to 3 metres, by methods that may be called 

 eleclrolechnical. Waves shorter than 300 cm., frequencies higher 

 than 10* cycles, are not easily produced by an>' such method; for if 

 one uses excessively small condensers and inductance-coils in the 

 hc)|)e of forcing the circuit-frequency much past lO", or even omils 

 coils and condensers altogether, it is found that the auxiliary ap- 

 paratus, the audion, e\en the wires of the circuit themselves, possess 

 capacities and inductances which cm not be annulled and which 

 hold the osciilation-frequcncN' down. H\' dex'ising oscillating svslems 

 which have scarcely any outward resemblance to the circuits of 

 familiar experience (although a formal analog]," can be established) 

 Hertz and his successors generated electromagnetic waves of fre- 

 quencies up to 10" and wavelengths down to 3 mm. Beyond a certain 

 gap there commences, near frequency 10'- and wavelength 0.3 mm., 

 the far-flung spectrum of rays emitted by molecules and atoni>. 

 This interval is one of the two lacunae in the complete electromag- 

 netic spectrum extending from lO'' past 10'-" cycles, which were men- 

 liimed in the preceding article of this series. Unlike the gap between 

 the uiira-\iolet and the X-ra\'s, it is not believed to be iioi)ulatc<l 

 by rays resulting from important processes occurring within the 

 atoms, nor do we know of any other peculiar type of radiation which 

 shoulfi be sought within it; and perhaps the bridging of it. wiieii 

 finally and untiuestionably achieved, will be held notable cliielK .is 

 a feat of experimental technique or a tour de force. On the other 

 hand, so long as the gap remains unspanned, we can hardh- dismiss 

 the i)ossibility that something in the order of nature may reser\e 

 one range of wa\elengths for the "natural" rays resulting from atomic 

 processes, anil liinii the ".irtiricial" waxes gener.d)le li\' eleclrolechnical 



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